1. Field of the Invention
The present invention relates to monofunctional polysiloxanes having a branched structure, and processes for preparing the same. The branched monofunctional polysiloxanes are useful in electrophotographic operations to prevent adhesion of toner to the surface of a fuser member. In particular, the present invention is directed to coating compositions comprising branched monofunctional polysiloxanes. Additionally, the present invention is directed to a fuser member or other substrate comprising branched monofunctional polysiloxanes.
2. Background of the Invention and Related Information
Polysiloxanes are widely used in electrophotography as polymeric release agents to prevent adhesion of toner to the fuser member and deter toner offset. The polysiloxanes have anti-adhesive properties which are favorable to protect the surface of the fuser member and maintain the durability of the fuser member.
Modified polysiloxanes having functional groups provide a protective barrier by attaching to the fuser or toner surface via covalent bonds, hydrogen bonding, polar bonding, or other interaction between the functional groups and the fuser or toner surface. The interaction of the functional groups with the fuser or toner surface allows the polysiloxane to sterically block contact of the toner with the fuser member surface and provide a protective barrier. Monofunctional polysiloxanes with one reactive functional group may interact with the fuser member surface to provide a protective coating as well as increase the wetting of non-functional components in the polymeric release agent composition. Multifunctional polysiloxanes with more than one reactive group also interact in the same manner to provide a protective coating; however, the presence of more than one functional group may allow undesired simultaneous interaction with components other than the fuser surface such as toner. This simultaneous interaction can cause undesirable toner contamination of the fuser surface.
Functional polysiloxanes are described in U.S. Pat. No. 4,101,686 to Strella et al. which discloses polymeric release agents having functional groups such as carboxyl, hydroxy, epoxy, amino, isocyanate, thioether or mercapto groups. The polymeric release agents are applied to a heated fuser member to prevent toner adhesion. Similarly, U.S. Pat. No. 4,272,179 to Seanor and U.S. Pat. No. 4,264,181 to Lentz et al. disclose polymeric release agents having functional groups which are applied to the surface of a fuser member.
Additionally, U.S. Pat. Nos. 5,141,788 and 5,281,506 to Badesha et al. disclose a fuser member comprising a polyorganosiloxane having reactive functional groups which is grafted to the surface of the cured fluoroelastomer layer. U.S. Pat. No. 4,853,737 to Hartley et al. also discloses a fuser roll with an outer layer comprising a cured fluoroelastomer having polydiorganosiloxane segments that are covalently bonded to the backbone of the fluoroelastomer. The polydiorganosiloxanes have functional groups in which at least one of the functional groups are present on the polydiorganosiloxane chain to form the covalent bond to the fluoroelastomer backbone.
Furthermore, monoamino functional polyorganosiloxanes are disclosed in U.S. Pat. Nos. 5,531,813 and 5,512,409 to Henry et al. in which the monoamino functionality interacts with the hydrofluoroelastomer surface of a fuser member to provide a barrier to the toner as well as a low surface energy film to release the toner from the surface. Also, branched T-type monoamino functional polysiloxanes in which the reactive group is attached to a central silicon atom are disclosed in U.S. Pat. No. 5,516,361 to Chow et al.
Despite the interaction of the functional groups to the fuser surface to provide a protective barrier, polysiloxanes having one or more reactive functionalities may also react with the toner and/or paper components. For example, polysiloxanes with more than one functional group per molecule may react with other components such as paper debris and form an undesirable gel on the fuser surface. Also, the functional polysiloxane may react with both the fuser and toner or debris, and act as a glue to provide a contaminated coating on the fuser member.
Once a desired toner-formed image is fixed in its intended location on a receiver, such as paper, it may be subjected to contact by other surfaces that will cause displacement of toner therefrom. This displacement may be in the form of smearing and/or transfer to the contacting surface, and is referred to as toner marking.
It is known that toner marking can be combated by a number of methods. Among these are including wax additives in the toner, increasing the toughness of the toner, adding release lubricants to the toner surface, and reducing the force of contact causing the toner marking. Such release lubricants added to toner have included functional polysiloxanes.
Additionally, functional polysiloxanes with a linear chain provide a protective barrier by forming a mushroom shape above the functional group attachment site; however, shear force can deform the shape and stretch the polymeric chain to expose the previously protected surface. Functional polysiloxanes with a branched chain may provide more resistance to shear force and prevent being stretched physically into a simple thin, linear chain; however, a bulky branched group may sterically impede interaction of the functional group with the surface.
Numerous attempts have been made to improve toner offset with functional polysiloxanes; however, there still remains a need in the art for polysiloxanes with anti-adhesive properties which provide good protection of the fuser surface without interaction with both the toner, fuser and/or debris. The present invention provides functional polysiloxanes which protect the fuser member and toned image surface with resistance to shear force, and without steric hindrance to allow effective interaction of the functional group with the fuser surface.